1. Field of the Invention
The present invention relates generally to determining the position of an automotive convertible top. More particularly, the present invention relates to a sensing system for determining a convertible top position based on magnetic field intensity and automatically adjusting a radio output parameter based on the convertible top position.
2. Discussion
In the automotive industry, a particularly popular luxury item is the convertible top. The ability of convertible tops to provide passengers with natural sunlight has always been a unique alternative to hard top vehicles. It is not surprising, however, that convertibles have a number of design considerations not encountered with conventional hard top automobiles. For example, it is commonly accepted that radio volume needs to be adjusted in accordance with the position of the convertible top. This requirement is mainly due to the fact that ambient noise and wind make it more difficult for passengers to hear the radio when the top is down.
Some automotive body control modules have addressed this concern by adding an operator selectable relay or switch to the vehicle and providing two separate volume and equalization curves for the radio. Thus, when the switch is positioned to indicate that the convertible top is in the down position, the body control module (BCM) selects the top down curve, which has a higher output level and equalization profile over the frequency spectrum of interest. When the operator positions the switch to indicate that the convertible top is in the up position, the top up curve is selected.
A difficulty with the above approach is the added cost to the vehicle associated with the position sensing switch and related circuitry and wiring. This additional cost substantially increases the overall cost of the vehicle, and has traditionally reduced convertible sales. It is therefore desirable to provide a mechanism for determining a convertible top position which does not significantly add to the overall cost of the vehicle.
Reliability concerns also accompany mechanical switches. In fact, it is not uncommon for convertible top switches and relays to require substantial alignment and positioning adjustments during both manufacturing as well as maintenance. It is therefore desirable to reduce error due to an increased number of parts.
Another design consideration associated with convertibles is drive control of the convertible top. For example, the motorized drive electronics must be able to determine when the top has reached the fully up or fully down position. Once again, under conventional approaches, switching circuitry has been placed in the vehicle to provide position information for control purposes. Such an approach is often ineffective and prone to device failures. It is therefore desirable to provide an effective mechanism for controlling movement of convertible tops.